4 


vj 


^^^"^^-^^ 


Issued  January  9,  1911. 


u.  s.  dp:partment  of  agriculture, 

BUREAU   OF   ENTOMOLOGY— CIRCULAR   No.  131. 

L.  O.  HOWARD.  Entomologist  and  Chiel  of  Bureau. 


HOW  TO  CONTROL  THE  PEAR  THRIPS. 


S.  W.  FOSTER  AND  P.  J{.  JONES, 

Agents  and  Experts. 


WASMIMGTON  :  GOVERNMENT  PRINTING  OFFICE  ;  1911 

G7859-'-Cir.  131-11 1 


A  33 


B  UREA  U  OF  ENTOMOLOG  Y. 

L.  O.  Howard,  Entomologist  and  Chief  of  Bureau. 

C.  L.  Maklatt,  Assistant  Entomologist  and  Acting  Chief  in  Absence  of  Chief. 

R.  S.  Clifton,  Executive  Assistant. 

W.  F.  Tastet,  Chief  Clerk. 

F.  H.  Chittenden,  in  charge  of  truck  crop  and  stored  product  insect  investigations. 

A.  D.  Hopkins,  in  charge  of  forest  insect  investigations. 

W.  D.  Hunter,  in  charge  of  southern  Jie Id  crop  insect  investigations. 

F.  M.  Webster,  in  charge  of  cereal  and  forage  insect  investigations. 

A.  L.  QuAiNTANCE,  in  charge  of  deciduous  fruit  insect  investigations. 

E.  F.  Phillips,  in  charge  of  bee  culture. 

D.  Al.  Rogers,  in  charge  of  preventing  spread  of  moths,  field  work. 
RoLLA  P.  Currie,  in  charge  of  editorial  work. 

Mabel  Colcord,  librarian. 

Deciduous  Fruit  Insect  Investigations. 

A.  L.  QuAiNTANCE,  w  charge. 

Fred.  Johnson,  S.  W.. Foster,  E.  L.  Jenne,  P.  R.  Jones,  A.  G.  Hammar, 
C.  \V.  Hooker,  J.  R.  Horton,  W.  Postiff,  J.  B.  Gill,  agents  and  experts. 

E.  W.  Scott,  J.  F.  Zimmer,  entomological  assistants. 
tCir.  131J 

(n) 


Circular  No.  1  31 .  Issued  January  9,  1911. 

United  States  Department  of  Agriculture, 

BUREAU  OF  ENTOMOLOGY. 

L.  O.  HOWARD,  Entomologist  and  Chief  of  Bureau. 


HOW  TO  CONTROL  THE  PEAR  THRIPS.« 

(Euthrips  pi/ri  Daniel.) 

By  S.  W.  P'osTER  and  P.  R.  Jones, 

Agents  and  Experts. 

DISTRIBUTION. 

The  pear  thrips  (Euthrips  pyri  Daniel)  (fig.  2)  is  at  present  confined 
to  California  and  is  very  destructive  throughout  Santa  Clara,  Contra 
Costa,  Solano,  and  Sacramento  counties,  with 
considerable  areas  infested  in  Alameda,  Yolo, 
Napa,   and   Sonoma  counties.      (Fig.  1.)     Re- 
ports of  the  presence  of  this  species  in  other  sec- 
tions of  California  and  in  Oregon  have  been  re- 
ceived, but  each  case  was  closely  investigated 
and  the  insect  in  question  found  to  be  some  other 
species.     Bagnal^  reports  this  insect  in 
England;   otherwise   it   is    not   known 
outside  the  State  of  California. 

ECONOMIC  IMPORTANCE. 


Fig.  1.— Map  showing  area  infested  by  pear  thrips  in  California. 
(Original.) 


suddenness  of  attack  in  great  numbers 


The  pear  thrips  is  at  present  tne 
most  important  in- 
sect pest  with  which 
the  growers  of  de- 
ciduous fruits  in  the 
counties  mentioned 
have  to  contend. 
On  account  of  the 
minute  size  of  the 
insect,  the  rapidity 
of  its  spread  over 
large  areas,  and  the 
completely  blasting  in  a  few 


«  The  present  paper  is  an  abstract  of  a  more  comprehensive  report  on  the  life  history 
and  control  of  the  pear  thrips  to  be  published  later.  The  recommendations  given  are 
based  on  the  results  of  experiments  carried  out  in  the  principal  centers  of  infestation 
since  the  fall  of  1908  to  and  including  the  summer  of  1910. 

&  Journal  of  Economic  Biology,  vol.  4,  No.  2,  1909, 


2  HOW   TO   CONTROL   THE   PEAR   THKIPS. 

days  all  prospects  for  a  crop  of  fruit — the  control  of  this  pest  is  a 
matter  of  considerable  difficulty. 

As  the  insect  is  each  year  extending  its  range  of  food  plants,  its 
capabilities  for  dissemination  are  correspondingly  increased.  There 
is  no  reason  to  believe  that  the  insect  will  disappear  in  a  few  years, 
but  it  should  be  regarded  as  a  permanent  pest  and  at  once  realized 
that  only  the  most  careful  attention  each  3"ear  to  necessary  control 
measures  will  make  it  possible  to  continue  the  profitable  culture  of 
deciduous   fruit    in    infested    orchards. 

Conservative  estimates  place  the  damage  caused  by  the  pear 
thrips,  in  the  Santa  Clara  Valley  alone,  during  the  j^ears  from  1904 
to  1910  at  nearly  $2,000,000,  while  the  loss  for  the  entire  State  during 
this  period  probably  exceeds  $3,500,000.  It  is  safe  to  say  that  the 
thrips  in  the  absence  of  treatment  would  cause  an  average  yearly 
loss  to  the  State  of  over  $1,000,000.  Also  each  additional  year  an 
increase  of  several  hundred  thousand  dollars  is  to  be  expected,  due 
to  the  increase  of  area  infested  and  the  greater  losses  in  the  areas 
previously  infested. 

CHARACTER  OF  INJURY. 

Injury  to  the  various  fruit  trees  b}^  this  species  is  caused  b}"  the 
feeding  of  the  adults  on  the  developing  buds  and  early  blossoms;  by 
the  deposition  of  eggs  into  the  fruit  stems,  leaf  stems,  and  newly 
formed  fruit,  and  by  the  feeding  of  the  larvae  in  the  blossoms  and 
on  the  young  fruits  and  foliage.  On  pears  the  greater  injury  is  pro- 
duced by  the  adults,  which  often  prevent  the  trees  from  blooming, 
while  on  prunes  and  cherries  the  larvae  frequently  prevent  a  crop  of 
fruit  from  setting  after  the  trees  have  come  into  full  bloom.  Also, 
the  deposition  of  eggs  into  the  fruit  stems  of  primes  and  cherries  so 
weakens  the  stems  that  much  of  the  young  fruit  falls.  The  feeding 
injury  is  not  produced  by  a  biting  or  chewing  process.  By  rasping  the 
tender  surfaces  in  the  developing  fruit  buds  and  the  young  fruits  with 
their  hardened  or  chitinous  mouthparts,  the  thrips  rupture  the  skin, 
causing  an  exudation  of  sap  whicli  is  often  followed  by  more  or  less 
fermentation,  especially  before  blooming.  The  feeding  by  larvae 
on  prunes  after  blooming  causes  the  well-known  thrips  ^^scab," 
while  most  ()f  the  scarred  and  misshapen  pears  are  caused  by  the  work 
of  the  a(hdts. 

LIFE  HISTORY. 

Adults. — The  a(hdts  (fig.  2)  or  winged  form  of  the  thrij)s  first 
appear  on  the  trees  about  tlie  JiiidcUe  of  February  and  emergence 


HOW   TO   CONTROL  THE   PEAR  THRIPS.  3 

from  the  ground  continues  till  early  April,  maximum  emergence, 
however,  occurring  in  late  February  and  early  March.     Examina- 


FiG.  2.— The  ppar  thrips  ( Euthrips  pyrl):  Adult,  greatly  enlarged.     (Original.) 

tion  of  the  tables  of  emergence  records  (Tables  I  to  V)  will  show  the 
dates  of  emergence  for  1909-10: 

Table  I. —  Total  daily  emergence  of  thrips  from  all  cages  at  laboratory,  San  Jose,  Cal., 

J 909  and  19 W. 


Number 

Number 

.  Number 

Number 

Date. 

thrips 

thrips 

Date 

thrips 

thrips 

emerging 

emerging 

emerging 

emerging 

in  1909. 

in  1910. 

in  1909. 

in  1910. 

Feb.  9 

0 

25 

Mar.  8 

219 

275 

10 

0 

18 

9 

776 

144 

11 

0 

16 

10 

497 

100 

12 

0 

16 

11 

498 

73 

13 

0 

4 

12 

338 

179 

14 

0 

88 

13 

313 

45 

15 

18 

22 

14 

248 

20 

16 

0 

27 

15 

279 

7 

17 

52 

34 

16 

259 

4 

18 

192 

33 

17 

152 

20 

19 

192 

14 

18 

42 

7 

20 

169 

23 

19 

61 

2 

21 

75 

62 

20 

28 

2 

22 

23 

24 

25 

26 

27 

28 

Mar.  1 

2 

3 

4 

5 

6 

119 
135 
552 
459 
444 
414 
781 
781 
535 
1,299 
714 
508 
362 
438 

129 

375 

272 

297 

4.55 

574 

657 

1,975 

3,592 

3,011 

4,217 

1,402 

1,595 

539 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

Apr.   1 

2 

3 

2 
6 
13 
3 
2 
3 
7 
7 
0 
2 
0 
3 
0 
1 

1 

1 

4  HOW   TO   CONTROL  THE  PEAR  THRIPS. 

Emergexce  Record  for  Contra  Costa  County. 

Table  II. — Emergence  of  thrips  from  cages  placed  in  ground  under  trees  in  pear  and 
prune  orchards,  Walnut  Creek,  Cal. 


1909. 

1910. 

Number 

Number 

Date. 

of  thrips 

Date. 

of  thrips 

i 

emerging. 

emergmg. 

1    Feb.  13 

0 

Feb.  21 

1 

16 

20 

23 

4 

19 

37 

25 

23 

22 

30 

27 

36 

26 

110 

Mar.   1 

56 

Mar.  2 

615 

3 

237 

5 

679 

5 

1,170 

10 

752 

7 

2,110 

12 

273 

9 

892 

16 

65 

11 

1,773 

20 

33 

13 

557 

22 

4 

15 

198 

27 

11 

17 

71 

19 

3 

21 

6 

27 

5 

Table  III. — Emergence  of  thrips  from  soil  samples  taken  from  orchard  in  November  and 
December  and  kept  in  cages  at  laboratory,  Walnut  Creek,  Cal. 


1909. 

1 

1910. 

Number 

Number 

Date. 

of  thrips 

Date. 

of  thrips 

out. 

out. 

Feb.  12 

3 

Feb. 18 

11 

15 

42 

20 

16 

16 

56 

22 

0 

17 

38 

24 

12 

18 

56 

26 

30 

20 

89 

1             28 

75 

23 

125 

Mar.  2 

377 

25 

185 

4 

918 

27 

246 

« 

937 

Mar.    1 

196 

8 

165 

4 

237 

10 

114 

7 

51 

1              12 

47 

10 

52 

14 

0 

14 

13 

16 

4 

19 

0 

22 

0 

Emergence  Record  for  Solano  County,  1910. 

Table  IV. — Emergence  of  thrips  from  cages  placed  in  ground  under  trees  in  orchards 

Suisun.  Cal. 


Number 

Number 

Date. 

of  thrips 

Date. 

of  thrips 

emerging. 

emerging. 

Fel).  17 

3 

Feb.  27 

20 

19 

0 

Mar.  1 

47 

21 

0 

3 

121 

23 

0 

10 

484 

25 

' 

16 

1 

HOW    TO    CONTROL   THE    PEAR   THRIPS. 


Table  V. — Emergence  of  thrips  from  samples  taken  from  orchard  in  November  and  Decem- 
ber and  kept  in  cages  at  laboratory,  Suisun,  Cal. 


Number 

Number 

Date. 

of  thrips 

Date. 

of  thrips 

emerging. 

emergmg. 

Feb.  16 

1 

26 

11 

17 

3 

27 

14 

18 

2 

28 

41 

19 

6 

Mar.    1 

105 

20 

1 

2 

247 

21 

1 

3 

243 

22 

4 

7 

612 

23 

2 

12 

357 

24 

5 

16 

82 

25 

11 

19 

8 

Fig.  3.— The  pear  thrips:  Eggs,  high- 
ly magnified.     (Original.) 


By  the  time  the  fruit  buds  have  swollen  sufficiently  to  separate 
the  bud  scales  slightly  at  the  tip  the  adults  force  their  way  within, 
feeding  upon  the  tenderest  portions  inside  the  buds.  When  the 
thrips  are  present  in  sufficient  numbers  the 
buds  are  completely  destroyed  and  the  trees 
fail  entirely  to  bloom. 

Eggs. — As  soon  as  the  first  leaf  surfaces 
or  fruit  stems  are  exposed  egg  laying  usually 
begins,  depending  somewhat  on  the  variety 

of  fruit  attacked. 
The  first  eggs  are 
deposited  the  last 
days  of  February 
and  oviposition 

continues  till  near  the  middle  of  April,  being 
at  its  maximum,  however,  from  the  lOtli  of 
March  to  the  1st  of  April.  Most  of  the  eggs 
(fig.  3)  are  deposited  just  under  the  epidermis 
in  the  fruit  stems,  young  fruit,  and  leaf 
stems.  The  eggs  require  from  five  to  seven- 
teen days  to  hatch,  the  average  time  being 
about  eight  days. 

Larvx. — By  the  time  the  trees  are  break- 
ing into  full  bloom  the  adults  have  done 
most  of  the  damage  caused  by  their  feeding, 
and  oviposition  is  at  its  height.  Many  of 
the  earlier  appearing  adults  are  dying  off  and 
larvae  (fig.  4)  are  beginning  to  appear  in 
Larva,  numbcrs.  The  very  first  larvae  can  usually 
be  found  about  March  20,  and  are  in  maxi- 
mum numbers  on  the  trees,  feeding  on  the  small  fruit  and  young 
foliage,  from  the  first  to  middle  of  April.  Reaching  their  full  devel- 
opment, the  larvae  drop  from  the  trees,  of  their  accord  or  with  falling 
calyces,  or  are  blown  by  wind  or  knocked  off  by  rain.     After  the 


Fig.  4.— The   pear   thrips 
greatly  enlarged.    (Original.) 


HOW    TO    CONTROL   THE   PEAR   THRIPS. 


middle  of  April  the  number  on  the  trees  diminishes  rapidly,  and  by 
the  last  of  April  all  the  larvae  are  off  the  trees  and  in  the  ground. 
Here  they  work  down  into  the  first  3  or  4  inches  of  hard  soil  below 
the  loose  surface  mulch  and  construct  a  tin}^  cell,  where  they  remain 
until  the  following  spring. 

Puyse. — The  larvae  mostly  remain  as  such  in  these  cells  till  Sep- 
tember, when  pupation  begins,  pupae  (fig.  5)  being  most  abundant 
during  October  and  November.  Many  adults  can  be  found  in  the 
ground  in  December,  and  by  the  1st  of  January  practically  all  the 
thrips  are  in  the  adult  stage  and  apparently  ready  to  emerge  and  go 
into  the  trees  whenever  conditions  are  right.  Broadly  speaking,  the 
thrips  spend  two  months  of  the  year  in  the  adult,  egg,  and  larval 

condition  on  the  trees  and  the  other 
ten  months  of  the  year  as  larvae, 
pupae,  and  adults  in  the  ground. 

CONTROL  MEASURES. 

The  pear  thrips  is  in  some  respects 
an  unusual  insect  in  that  it  remains 
in  a  dormant  or  semidormant  condi- 
tion for  about  ten  months  of  the  year. 
Although  on  the  trees  for  only  two 
months  out  of  the  twelve,  it  is  able 
in  this  short  time,  in  the  absence  of 
treatment,  to  completely  destroy  all 
prospects  of  a  crop  of  fruit,  in  many 
cases  within  a  very  few  days.  The 
trees  are  attacked  at  the  period  of 
bud  swelhng  and  blossoming,  when 
they  are  most  susceptible  to  injury. 
These  minute  insects  come  literally 
in  swarms,  and  may,  if  left  alone, 
completely  destroy  all  of  the  fruit 
buds  of  an  orchard  in  four  or  five  days.  Many  cases  have  been 
known  where  a  delay  of  four  or  five  days  in  spraying  resulted  in 
loss  of  the  entire  crop  of  fruit,  and  in  some  cases  half  of  all  the 
buds  were  killed  in  three  days  after  the  thrips  appeared  on  the  trees 
in  great  numbers.  In  view  of  this  condition  it  is  very  evident  that 
any  means  of  control  must  be  very  thorough  and  done  in  the  most 
exacting  manner  at  the  proper  time. 

EXPERIMENTS  IN  THRIPS  CONTROL. 

Many   experiments  with   soil   fmnigaiits,  fertilizers,  and  irrigation 
were  made  with  the  hope  of  killing  the  thrips  while  in  the  ground, 


Fig.  5.— The  pear  thrips:  Pupa,  greatly 
enlarged.    (Original.) 


HOW   TO   CONTROL  THE  PEAR  THRIPS.  7 

but  all  of  them  have  proved  to  be  absolutely  of  no  avail,  or  at  most 
impractical  and  expensive.  In  most  cases  the  general  vigor  and 
health  of  the  trees  were  improved  by  early  fall  irrigation  and  by  the 
application  of  fertihzers. 

CULTIVATION. 

Thorough  plowing  in  the  fall  in  prune  orchards  planted  on  gravelly 
and  sandy  soils  gave  very  helpful  results.  Success  by  deep  plowing, 
cross  plowing,  and  harrowing  in  October  and  November  was  fairly  gen- 
eral in  all  experiments  tried  in  Santa  Clara  County  in  the  fall  of  1908 
and  1909.  This  manner  of  cultivation,  when  carried  out  to  a  depth 
of  from  7  to  9  inches,  resulted  in  killing  from  60  to  80  per  cent  of  the 
thrips  present  in  the  soil,  but  was  not  a  sufficient  control,  as  enough 
thrips  escaped  to  cause  great  injury  to  the  buds  the  following  spring. 

SPRAYING. 

A  long  list  of  insecticides  was  tried  out  in  spraying  experiments, 
both  in  the  laboratory  and  by  spraying  the  trees  in  the  spring.  All 
poison  sprays  had  to  be  al^andoned  because  of  the  inability  to  poison 
the  thrips,  as  })oth  adults  and  larvae  do  not  feed  in  a  way  to  be  sub- 
ject to  poisoning.  Sticky  sprays  were  difficult  to  apply  and  proved 
ineffective,  as  they  do  not  retain  this  quality  long  and  the  thrips 
seem  capable  of  moving  around  on  almost  any  kind  of  surface.  Dust 
sprays  and  preventive  sprays  had  to  be  abandoned  because  the  dust 
sprays  failed  to  kill  and  the  rapid  swelling  of  buds  and  continued 
appearance  of  new  surface  area  gave  the  thrips  plenty  of  feeding 
ground  and  exposed  phices  of  entrance  into  the  buds.  Success  with 
contact  sprays  seemed  more  apparent;  of  these,  various  caustic 
sprays,  such  as  caustic-soda  and  carbolic-acid  solutions,  gave  excel- 
lent results  in  killing  the  thrips,  but  were,  as  a  rule,  unsafe  because 
of  injury  to  the  trees. 

Solutions  of  tobacco  extract  were  very  promising,  and  when  used 
at  sufficieat  strengths  killed  all  the  thrips  actually  reached,  but  they 
lacked  sufficient  penetrating  quality  to  enter  the  swelling  buds,  a  con- 
dition absolutely  necessary,  especially  on  pears,  as  most  of  the  injury 
is  done  inside  the  cluster  buds.  Mechanical  mixtures  of  various 
mineral  oils  and  animal-oil  soaps  were  tried  and  abandoned  because 
of  the  difficulty  of  keeping  them  thoroughly  mixed  and  the  resulting 
injury  to  the  trees  caused  by  free  oil  separating  out.  Fish-oil  soap 
emulsions  with  these  various  oils  gave  better  results,  the  raw  distil- 
lates running  from  30°  to  40°  Baume  being  decidedly  preferable  over 
either  the  kerosenes  or  the  heavy  crude  oils. 

A  distillate-oil  emulsion  made  according  to  directions  (see  pages 

8-10)  gave  better  penetration  into  the  swelling  pear  buds  than  any  other 

material  which  has  been  tried.     There  was  one  drawback,  however; 

when  this  emulsion  was  used  in  sufficient  strengths  to  kill  all  the 

67859°— Cir.  131—11 2 


8  HOW   TO   CO^^TROL   THE   PEAR   THEIPS. 

thrips  present  or  even  a  large  percentage  of  them,  there  was  consid- 
erable oil  injur}^  to  the  buds.  It  was  found  that  the  weaker  emulsions 
of  from  3  to  6  per  cent  strengths  had  all  the  desired  penetrating  quali- 
ties and  \nth  Httle  or  no  injurious  effect  upon  the  trees.  As  the  nico- 
tine solutions  killed  all  the  thrips  present  and  gave  no  spray  injury 
tliis  led  to  a  combination  of  the  two  in  Contra  Costa  County  in  the 
spring  of  1909  Tsdth  most  satisfactory  results. 

A  tobacco  extract  containing  23  per  cent  nicotine,  diluted  at  the 
rate  of  1  to  60  in  a  6  per  cent  distillate-oil  emulsion,  Idlled  all  the 
thrips  touched  and  penetrated  well  into  the  pear  cluster  buds.  The 
pubescent  covering  of  the  individual  buds  in  the  cluster,  being  resist- 
ant to  water,  seemed  to  act  on  the  dilution  in  distillate-oil  emul- 
sion in  much  the  same  manner  as  the  wick  upon  oil  in  a  lamp.  Vari- 
ous other  combinations  of  nicotine  solutions  \\ith  'Mime  and  sulphur 
solutions"  and  'Mysol  solutions"  and  ''soap  solutions"  were  tried 
extensively,  but  none  proved  to  be  as  effective  and  at  the  same  time 
as  practical  as  the  combination  of  distillate-oil  emulsion  and  the  nico- 
tine solutions. 

DISTILLATE-OIL   EMULSION. 

Homemade  preparation. — Because  of  its  cheapness  and  greater 
efficiency  as  a  penetrating  spray,  and  therefore  a  more  satisfactory 
killing  agent,  growers  are  strongly  advised  to  make  their  own  emul- 
sions and,  preferabl}',  the  soap,  although  the  latter  can  usually  be 
depended  on  if  bought  from  reliable  dealers. 

Directions  for  molcing. — To  make  soap  use  this  formula  or  some 
multiple  of  same: 

Water G  gallons. 

Lye  (98  per  cent) 2  j)<)un(ls. 

Pish  oil \\  gallons. 

Put  the  water  in  a  caldron  or  boiler  and  add  the  lye.  When  the  lye 
is  thoroughly  dissolved  and  the  water  boiling,  pour  in  the  fish  oil,  stir- 
ring in  the  meantime,  and  boil  slowly  for  two  hours.  When  the  soap 
has  boiled  sufficiently  it  should  give  a  ropy  effect  when  stirred  and 
brought  up  upon  the  ladle.  This  formula  gives  about  40  ])()un(ls  of 
moderately  firm  soap. 

Growers  are  cautioned  to  buy  only  genuine  fish  oil  and  not  a  fish- 
oil  compound  or  a  mixture  of  fish  oils  and  vegetable  oils.  Herein  lies 
part  .of  the  secret  of  the  penetrating  efiiciency  of  the  distillate  emul- 
sions made  by  using  animal-oil  soap  as  the  einulsifier.  The  cost  of 
the  soap  is  SO. 0105  per  pound  made  from  fisli  oil  at  35  cents  a  gallon. 

The  (hstillate-oil  stock  emulsion  should  be  made  as  follows: 

Formula:" 

Uot  water \'l  gallons. 

Kish-oil  or  whale-oil  soap 30  j)oun(ls. 

Distillate  oil  (raw)  'M)°  to  :i4°  r.aunie 20  gallons. 

a  For  a  spray  tank  of  200  gallons  capacity,  live  times  lliis  formula  can  be  made  at 
one  time. 


HOW    TO    CONTROL   THE    PEAR   THRIPS.  9 

Have  the  water  boiling  hot  when  put  into  the  spray  tank  and  add 
the  soap  immediately  while  the  agitator  is  running  at  a  good  speed. 
When  the  soap  is  all  thoroughly  dissolved,  pour  in  the  oil  slowly, 
keeping  the  mixture  well  agitated  while  the  oil  is  going  into  the  tank. 
When  all  the  oil  is  in  and  well  mixed,  pump  out  through  the  nozzles  at 
good  pressure  (not  less  than  175  pounds)  into  storage  tanks. 

No  one  should  attempt  to  make  this  stock  emulsion  without  a 
power  spraying  machine,  as  thorough  agitation  and  high  pressure  are 
important  requisites.  Also,  care  should  be  used  in  having  measure- 
ments reasonably  exact,  the  water  boiling  hot,  and  soap  thoroughly 
dissolved,  before  any  oil  is  put  in.  This  stock  emulsion  contains 
approximately  55  per  cent  oil,  and  to  make  a  3  per  cent  emulsion  use 
5h  gallons  of  this  stock  in  each  100-gallon  tank.  To  dilute,  first  put 
the  stock  emulsion  in  spray  tank  (have  the  agitator  going),  and  then 
add  the  water,  keeping  the  agitator  running  all  the  time.  Tliis  is 
important  with  the  commercial  preparations  as  well  as  with  the  home- 
made emulsions.  For  the  combination  sprays  of  oil  emulsions  and 
nicotine  solutions,  the  nicotine  should  be  added  last,  that  is,  after  the 
oil  emulsion  has  been  diluted  to  the  desired  strength.  These  solu- 
tions should  not  be  mixed  together  without  first  diluting  one  of  them. 

This  concentrated  emulsion  will  cost  the  grower  about  5  cents  per 
gallon,  as  most  of  the  various  distillates  used  for  spraying  cost  from 
5  to  10  cents  a  gallon  in  drum  lots. 

In  the  spraying  season  of  IDIO  many  growers  of  Contra  Costa 
County  experienced  great  difficulty  in  making  emulsions  that  would 
remain  emulsified  when  diluted.  Part  of  this  trouble  was  due  to  the 
varying  degrees  of  hardness  in  the  water,  but  more  to  the  composition 
of  the  oil,  especially  where  the  treated  oils  and  in  some  cases  ordinary 
stove  distillates  were  used.  Even  after  these  treated  oils  were  emul- 
sified by  changing  the  amount  of  soap  used  and  treating  the  water 
to  ''soften"  it,  the  result  was  not  satisfactory,  as  the  diluted  emulsion 
from  this  lacked  the  essential  penetrating  quality  and  had  a  tendency 
to  collect  in  large  drops  rather  than  to  spread  out  in  a  thin  film. 

Experiments  conducted  thus  far  indicate  that  success  is  more 
uniformly  obtained  by  using  an  untreated  raw  distillate  32°  to  34° 
Baume  with  comparatively  high  flashing  point.  Some  of  the  treated 
oils  have  given  good  results,  but  as  a  whole  the  untreated  raw,  straight 
distillates,  comparatively  free  from  naphtha  and  with  a  high  flashing 
point,  have  given  far  better  and  more  general  satisfaction. 

Some  of  the  oil  companies,  particularly  in  the  Bakersfield  and 
Coalinga  districts,  put  out  raw  short-cut  distillates — that  is,  the  first 
distillate  after  the  naphtha,  gasolines,  etc.,  have  been  removed. 
This  kind  of  oil  when  running  32°  to  34°  Baume  should  under  all  cir- 
cumstances be  given  preference.  The  ordinary  stove  distillates 
have  not,  as  a  rule,  given  as  good  satisfaction,  possibly  because  they 


10  HOW    TO   COXTEOL   THE   PEAR   THKIPS. 

contain  too  much  of  the  light  gaseous  oils,  which  lower  the  flashing 
point. 

There  are  several  commercial  preparations  of  oil  emulsions  and 
miscible  oils  on  the  market,  but  these  have  not  given  as  satisfactory 
results  against  the  adult  thrips  as  the  homemade  preparation,  espe- 
cially on  pears,  on  account  of  the  noticeable  lack  of  penetration  into 
the  cluster  buds.  Besides,  all  of  these  commercial  preparations  are 
far  more  expensive.  Allowing  25  cents  per  hour  for  labor  in  making 
the  soap  and  the  concentrated  homemade  emulsion,  the  commercial 
preparations  cost  the  grower  from  2  to  5  times  more  than  the  more 
efficient  homemade  preparation. 

COMMERCIAL  RESULTS. 

During  the  season  of  1909-10  many  large-scale  experiments  and 
demonstrations  were  carried  out  in  pear,  prune,  and  cherry  orchards 
to  determine  more  conclusively  the  efl'ectiveness  of  this  combined 
spray  and  to  put  the  treatment  on  a  commercial  basis;  also,  that 
growers  might  see  for  themselves  the  results  of  the  work  and  know 
the  monetary  gain  possible  by  such  control  measures  as  are  recom- 
mended. The  commercial  results  from  some  of  these  experiments 
are  given  below: 

PRUNES,  SANTA  CLARA  COUNTY. 

The  16-acre  prune  orchard  belonging  to  ^Ir.  P.  Landon,  situated 
in  the  Willows  district,  near  San  Jose,  CaL,  consists  of  some  of  the 
largest  and  finest  prune  trees  in  the  valley.  The  trees,  which  are 
about  25  years  old,  are  planted  20  feet  apart  and  the  branches  now 
overlap  between  the  rows.  The  orchard  has  very  heavy  sandy  loam 
and  has  been  well  cultivated  and  usually  irrigated  twice  each  year. 
Thrips  became  injurious  in  the  year  1906,  increasing  greatl3Mn  1907, 
and  causing  much  injury  over  the  entire  orchard,  so  that  instead  of  a 
normal  crop  of  a  hundred  or  more  tons  of  green  (unchied)  i)runes  the 
entire  16  acres  produced  only  IS  tons  of  green  fruit.  Injury  by  the 
thrips  was  worse  in  190.S,  the  yield  that  3'ear  being  only  10  tons  of 
green  prunes. 

Demonstration  fok   1909. 

Id  the  fall  of  19()S,  under  direction  of  the  Bureau  of  Entomology, 
Mr.  I^andon  plowed  and  cross  plowed  this  orchard  to  a  depth  of  9 
inches,  with  thorougli  liarrowing  after  each  plowing.  Thri})s  were 
very  abundant  in  the  soil,  there  being  sometimes  as  many  as  8,000 
to  the  scpiare  foot. 

The  following  table,  giving  the  emergence  of  adults  in  s|)ring  from 
samples  of  soil  taken  before  and  after  plowing,  shows  that  a])proxi- 
iiiately  70  percent  of  Ihe  thrips  were  killed  by  cultivation: 


HOW    TO    CONTROL   THE    PEAR   THRIPS. 


11 


Table  VI. — Number  of  adult  thrips  emerging  from  cages  containing  samples  of  soil 
taken  before  and  after  plowing — Landon  prune  orchard,  1908-9. 


Plowed  and  cross  plowed. 

Before  plowing. 

Cage  I.         Cage  II. 

Cage  III. 

Cage  IV. 

Cage  V. 

Cage  VI. 

475                 389 

607 

115 

1,175 

1,474 

Average  number  of  thrips  per  cage  before  plowing 1,  364 

Average  number  of  thrips  per  cage  after  plo\\'ing  and  cross  plowing 396 

Percentage  li\'ing  in  treated  areas  as  against  the  number  of  thrips  living  in  un- 
treated ground per  cent . .  30 

Approximate  percentage  killed do 70 

In  the  spring  of  1909,  5^  acres  of  this  16-acre  orchard  were  spraved 
three  times;  twice  before  blooming,  for  adults,  the  first  application 
March  8  and  9,  just  as  cluster  buds  were  spreading,  and  the  second 


Fig.  0.— Powlt  sprayer  at  work  in  Landon  prune  orchard,  1909.    (Original.) 

application  March  16  and  17,  just  as  the  white  tips  of  the  petals  were 
beginning  to  show.  The  third  application  or  larval  treatment  was 
put  on  April  11  and  12,  after  most  of  the  petals  had  fallen.  For  aU 
sprayings  a  gasoline-power  outfit,  with  tower  platform  and  three 
leads  of  hose,  as  sIiowtl  in  figure  6,  was  used,  two  men  spraying  from 
the  ground  and  one  from  the  tower  to  cover  the  tops  of  the  trees.  The 
material  used  was  tlie  recommended  3  per  cent  homemade  distillate- 


12 


HOW   TO   COXTROL   THE   PEAR  THRIPS. 


oil  emulsion  with  commercial  tobacco  extract  Xo.  1,  added  at  the 
rate  of  1-60,  and  the  cost  of  the  three  applications  was  $157.38,  the 
labor  required  in  spraying  being  three  men  at  $2  per  day  and  one 
team  at  $2.50  per  day,  making  a  total  of  $8.50  per  day,  or  a  total  of 
$51  for  the  six  days;  gasoline  for  the  engine  cost  $2.40;  plowing  and 
cross  plowing  the  previous  fall,  $26.65,  making  a  total  cost  of  $237.45 
for  the  combmed  treatment  of  plowing  and  spraying  the  5J  acres,  or 
$44.54  per  acre,  an  average  of  $0,449  per  tree. 

The  yield  from  tliis  plat  was  45  tons  of  green  prunes,  making  an 
average  yield  of  8.44  tons  per  acre,  or  155.17  pounds  per  tree.  The 
prunes  when  dried  averaged  54  to  the  pound,  giving  a  commercial 
value  for  the  plat  of  $1,710,  or  a  value  of  $320.82  per  acre,  or  an 
average  of  $2,948  per  tree,  as  the  prunes  were  sold  on  a  2J-cent  basis 
for  dried  prunes  averaging  80  to  a  pound. 

Plat  II. — The  rest  of  the  orchard,  comprising  10§  acres,  and  which 
only  had  the  plowing  and  cross  plowmg  in  the  fall  of  1908,  at  the  cost 


2_|^^^bk^ 


xS^ 


Fig.  7. — Diagram  showing  yield  in  green  prunes  i)er  acre  upon  the  sprayed,  plowed,  and  check  blocks, 
Landon  prune  orchard,  1909:  o.  Sprayed  and  plowed,  367.93  boxes,  value  $320.82  per  acre;  b,  plowed 
block,  8.5.G5  boxes,  value  S74.85  per  acre;  c,  check  block,  7  boxes,  value  $6.65  per  acre.    (Original.) 

of  $5  per  acre,  or  $0,046  per  tree,  yielded  21  tons  of  green  prunes,  or 
an  average  of  1.97  tons  per  acre,  or  36.45  pounds  per  tree,  giving  a 
commercial  value  of  the  plat  as  $798,  or  a  value  of  $74.85  ])er  acre, 
averaging  $0,692  per  tree. 

J*l(it  III,  check. — This  plat,  em])racing  5  acres  of  the  ])nme  orchard 
beloiigmg  to  Mr.  F.  Cottle,  and  immediately  adjoining  the  Landon 
orchard  and  of  the  same  kind  of  soil  and  with  similar  trees  in  re^rard 
to  size  and  ])re^d()us  care,  received  no  treatment  for  thri})s.  The  total 
yield  was  1,750  ])ounds  of  green  ])runes,  or  an  average  yield  of  350 
pounds  per  acre,  or  3.24  poimds  ])er  tree,  representing  a  commercial 
value  of  $33.25  for  the  plat,  or  an  average  of  $6.65  ])er  acre  or  $0.06 
])er  tree.  Tlie  yield  and  value  per  acre  upon  the  three  ])lats  is  shown 
diagrammatically  in  figure  7. 

Tlie  average  gain  j)er  acre  U})()ii  Plat  I  was  obtained  after  adding 
tlie  total  cost  of  treatment  per  acre  to  the  value  of  the  crop  ])cr  acre 
IVoiii  the  check  ])lat,  and  subtracting  tliat  amount  from  the  value  of 


HOW    TO   CONTROL   THE  PEAR  THRIPS.  13 

the  yield  per  acre  upon  Plat  I.  This  gave  a  net  gain  of  $269.53  per 
acre  as  returns  upon  an  investment  of  $44.54,  or  a  gam  of  about  600 
per  cent.  The  gain  upon  this  plat  due  to  the  spraying  alone  was 
$199.88  per  acre,  or  $1.85  per  tree. 

Plat  II,  which  received  only  the  plowing  and  cross  plowing,  gave, 
after  adding  the  cost  of  the  treatment  to  the  yield  per  acre  upon  the 
check  plat  and  subtracting  the  total  from  the  yield  per  acre  upon 
Plat  II,  a  gain  of  $63.20  per  acre  for  an  investment  of  $5,  or  about 
1,200  per  cent  on  the  investment. 

Owing  to  the  lateness  of  the  third  application  on  Plat  I,  the  larvae 
caused  considerable  scabbing  on  the  fruit,  and  the  difference  in 
quality  of  the  fruit  from  Plat  I  and  Plat  II  was  not  as  great  as  would 
have  been  the  case  had  the  larval  application  been  applied  a  few  days 
earher. 

Results,  1910. 

During  the  faU  of  1909  part  of  the  orchard  was  irrigated  and  the 
entire  16  acres  were  plowed  to  a  depth  of  8  inches  in  November.  One 
small  block  was  cross  plowed.  The  entire  orchard  was  harrowed 
several  times  after  the  plowing. 

Plowing  Results. 

Soil  samples  were  taken  in  similar  cages  as  in  the  previous  year  and 
yielded  the  following  results: 


Cage  No.  Treatment. 


II I  Before  plowing 

Il-a I  Plowed  once 

IV Before  plowing 

I V-a Plowecl  once 

I Before  plowing 

I-a Plowing  and  cross-plowing. 


Total 
number 
thrins. 


2,813 
3.53 
3.379 
1..306 
2,731 
27 


Per  cent 
killed. 


The  average  percentage  of  thrips  killed  by  one  plowing  was  71  per 
cent  and  the  average  number  killed  by  plowing  and  cross  plowing 
98  per  cent. 

No  spraying  was  done  in  1910,  except  a  few  trees  for  other  experi- 
ments. 

Results. — All  of  the  trees  on  the  16  acres  came  into  heavy  bloom, 
but  only  the  580  trees  of  Plat  I  and  one  block  of  about  80  trees  which 
was  sprayed  for  larvae  in  1909  set  a  heayy^  crop,  as  man}^  thrips  were 
present  in  the  rest  of  the  orchard.  The  trees  sprayed  in  1909  were 
stronger,  and  so  many  of  the  thrips  had  been  killed  by  the  treatment 
that  the  accumulative  results  showed  almost  as  great  a  difference  in 
the  crop  yield  for  1910  as  was  the  case  in  1909,  when  the  spraying  was 
actually  done. 

LIBRARY 


14  HOW   TO   CONTROL   THE   PEAR    THRIPS. 

The  primes  averaged  57  to  the  pound,  and  computations  made  on 
the  basis  of  5  cents  for  prunes  running  80  to  the  pound.  The  different 
yields  and  values  were  as  follows: 

Plat  I — Demonstration  Uoclc  of  1909,  consisting  of  580  trees. — This 
block  pelded  35  tons  212  pounds  of  green  prunes,  worth  $2,109.87 
for  580  trees,  or  $3.63  per  tree  or  $392.04  an  acre. 

Plat  II — Sprayed  for  larvx  in  1909,  80  trees. — This  block  yielded 
2  tons  676  pounds  of  green  prunes,  worth  $140.51  for  80  trees,  or  $1.99 
per  tree  or  $214.92  per  acre.     (This  was  part  of  Plat  II  in  1909.) 

Plat  III — Remainder  of  orchard,  consisting  of  10  acres,  not  sprayed 
in  1909. — This  block  pelded  1\  tons  of  green  prunes  worth  $450.75 
for  1,080  trees  or  10  acres,  making  $0,417  a  tree  or  $45,075  an  acre. 

An  examination  of  the  above  statement  of  yields  and  values  shows 
that  great  headway  can  be  made  the  first  year  in  eliminating  the 
thrips  injury  from  an  orchard  by  thorough  spraying  and  that  a  con- 
siderable benefit  extends  into  the  second  year. 

Demonstrations  for  1910. 

The  6J-acre  prune  orchard  belonging  to  Mr.  H.  Curry  was  plowed 
and  cross-plowed  in  November,  1909,  to  a  depth  of  11  inches  and  har- 
rowed after  each  plowing.  The  block  was  then  sown  to  barley  for 
a  cover  crop  wliich  made  a  good  growth  and  was  at  spraying  time 
nearly  3  feet  high. 

Examination  of  two  samples  of  soil  17  by  17  inches  square,  taken 
before  plowing,  and  two  of  the  same  size  taken  after  plowing,  showed 
tliat  approximately  61  per  cent  of  the  thrips  were  killed. 

Plat  A. — In  adcHtion  to  the  fall  plowing,  this  block  of  300  trees 
received  three  applications  of  commercial  tobacco  extract  No.  1  com- 
bined at  the  rate  of  1  to  66  with  3  per  cent  homemade  distillate-oil 
emulsion.  The  first  spraying  was  applied  March  7,  just  as  the  cluster 
buds  were  spreading.  The  second  for  adidt  thrips  was  made  March  1 7, 
as  the  tii)s  of  the  ])etals  were  showing.  The  third  application,  wliich 
was  for  the  larvie,  was  made  April  6,  after  most  of  the  ])ctals  had 
fallen.  In  all  of  the  spraying  an  effort  was  made  to  direct  the  spray 
into  the  end  of  each  bud  and  to  drench  the  trees  thoroughly. 

Plat  B. — This  plat,  consisting  of  98  trees,  received  the  cultivation, 
but  no  spraying. 

Results. — The  first  application  was  made  too  late  to  obtain  best 
results,  and  a  large  number  of  buds  w^as  so  far  advanced  that  it  was 
diflicult  to  reach  all  of  the  thrips.  A  series  of  counts  showed  that  all 
of  the  exposed  thrips  were  killed  and  about  30  per  cent  of  those 
within  the  buds.  The  second  application  killed  practically  all  the 
thrips  left  on  the  trees  (over  90  per  cent),  as  the  bud  clusters  were 
spreading  at  this  time.     A  fair  port  ion  of  the  blossoms  set  fruit  on  the 


HOW    TO    CONTROL   THE   PEAR   THRIPS. 


15 


sprayed  block  and  some  on  the  plowed  block,  but  the  fruit  on  the 
latter  continued  to  drop  until  picking  time.  The  yield  upon  the 
various  plats  is  shown  diagrammatically  in  figure  8,  and  was  as  follows: 

Plat  A  yielded  16,254  pounds  of  green  prunes,  or  8,127  pounds  of 
dried  prunes,  from  the  300  trees.  This  made  an  average  yield  of 
5,849.92  pounds  of  green  prunes  per  acre,  or  54.166  pounds  per  tree. 

Plat  B  yielded  1,032  pounds  of  green  prunes  or  516  pounds  of  dried 
prunes  from  the  98  trees,  or  an  average  of  1,138.32  pounds  per  acre, 
or  10.54  pounds  of  green  prunes  per  tree. 

Plat  C,  consisting  of  10  acres,  was  left  untreated  to  serve  as  a  check 
for  comparison,  and  yielded  860  pounds  of  green  prunes,  or  430  pounds 
of  dried  prunes,  for  the  1,080  trees.  This  gives  an  average  yield  of 
86.4  pounds  per  acre,  or  0.8  pound  of  green  prunes  per  tree. 


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Fig.  8.— Diagram  showing  yield  per  acre  in  green  prunes,  Curry  orchard,  1910:  a.  Sprayed  and  plowed, 
136.08  boxes,  value  $190.08  per  acre;  b,  plowed  block,  26.46  boxes,  value  s;j4.0'2  per  acre;  c,  check  block, 
2  boxes,  value  $2.59  per  acre.     (Original.) 

Scabbiness. — ^\n  examination  and  count  was  made  of  all  the  fruit 
from  5  trees  on  the  sprayed  ])l()('k  and  from  5  trees  in  the  iinsprayed 
block,  giving  the  following  results : 


I'lal. 


Total 
number 
prunes. 


Number 
clean. 


Number 
scabby. 


Per  cent 

free  from 

scab. 


Sprayed  block 

Unsprayed  block. 


10, 139 

826 


9.831 
0 


308 

826 


It  will  be  seen  from  the  above  table  that  the  sprayed  fruit  was  prac- 
tically free  from  scab  (the  4  per  cent  that  was  scabby  being  only  very 
slightly  marked),  while  the  unsprayed  fruit  was  all  badly  scabbed. 

Size  of  fruit. — Comparisons  of  the  sprayed  and  unsprayed  fruit 
when  dried  showed  the  former  to  average  50  prunes  to  the  pound  and 
the  unsprayed  60  to  the  pound,  making  a  difference  of  $10  a  ton, 
which  would  pay  nearly  lialf  the  cost  of  the  spraying. 

Value  of  the  crop. — As  all  of  the  values  of  the  prune  yields  for  1910 
have  been  figured  on  a  5-cent  basis  for  prunes  averaging  80  to  the 
pound  dried,  this  basis  is  here  employed,  although  the  crop  was  sold 
for  more  than  the  above  ({notation  and  })remiums  were  given  for  the 
large  size  and  quality  of  the  fruit. 


16  HOW   TO   COXTKOL   THE   PEAR   THRIPS. 

Plat  A,  wliicli  produced  16,254  pounds  of  green  prunes  from  300 
trees,  gave  a  crop  value  of  $528,255,  or  $1.7608  a  tree,  or  $190.08  an 
acre. 

Plat  B,  which  yielded  1,032  pounds  of  green  prunes  from  98  trees, 
gave  a  crop  value  of  S30.96,  or  S0.315  a  tree,  or  $34.02  an  acre. 

Plat  C,  which  yielded  860  pounds  of  green  prunes  from  1,080  trees, 
gave  a  crop  value  of  $25.80,  or  $0,024  a  tree,  or  $2,592  an  acre.    , 

Cost  of  spraying. — As  3,800  gallons  of  diluted  spray  material  wei-e 
used  for  all  three  sprayings  upon  Plat  A,  the  total  cost  at  S0.01625 
per  diluted  gallon  would  be  $61.75.  The  labor  and  gasoline  cost  2 
cents  a  tree,  each  application,  for  the  300  trees,  or  a  total  of  $18.  The 
total  cost  of  the  spraying  was  $79.75,  or  $0,265  a  tree,  or  $28.78  an 
acre  for  the  three  applications. 

Gain  due  to  spraying. — The  gain  due  to  the  spraying  would  be  ob- 
tained by  adding  the  value  of  the  crop  per  tree  on  Plat  B  to  the  cost 
of  the  spraying  and  subtracting  the  j)roduct  from  the  value  of  the 
crop  per  tree  of  Plat  A.  This  gives  a  gain  (hie  to  the  spraying  of  $1.18 
per  tree,  or  $127.44  an  acre. 

Other  Demonstrations. 

In  cooperation  with  or  working  under  the  advice  of  the  Bureau  of 
Entomology,  several  fruit  growers  in  Santa  Clara,  Contra  Costa, 
Solano,  and  Sacramento  counties  during  1910  gave  thorough  treat- 
ment to  portions  of  their  orchards  and  left  similarly  infested  areas 
untreated  without  any  protection  from  thrips  injury.  Many  of  these 
demonstrations  were  highly  successful,  but  for  lack  of  space  only  two 
of  these  are  recorded  herein  in  some  detail.  These  results  show  very 
conclusively  what  can  be  done  by  the  individual  growers  if  the  right 
material  is  i)roperly  applied  in  time  to  kill  the  thrips  before  the  buds 
have  been  destroyed,  and  that  the  treatment  will  increase  the  yield 
and  value  of  the  crop,  frequently  paying  several  hundred  per  cent 
on  the  investment. 

PEARS,    CONTRA    COSTA    COUNTY. 

Mi  orchard  consisting  of  about  5i  a,cres  of  Bartlett  pears  belonging 
to  John  Swett  &  Sons,  in  the  Alhambra  Valley,  near  Martinez,  Cal., 
had  been  badly  daniaged  by  thrips  for  three  years,  causing  almost 
total  failure  of  crop. 

In  the  spring  of  1910  :Mr.  Frank  T.  Swett  had  550  of  the  trees 
sprayed  twice  for  adults,  and  a  portion  of  these  received  a  third 
application  or  lar\'al  treatment.  All  spraying  consisted  of  the  rec- 
ojnmended  niaterial  (conimercial  tobacco  extract  No.  1  diluted  1  })art 
to  66  in  3  per  cent  honieniade  distillate-oil  (unulsion)  put  on  the  trees 
with  good  pressure,  using  gasoline-power  outfit  with  8-f()ot  tower, 
thus  enabling  one  jnan  to  cover  thoroughly  the  tops  of  the  trees  and 


HOW    TO    CONTROL   THE   PEAR   THRIPS. 


17 


clrencli  all  buds  pointing  upAvard  wliicli  could  not  be  properly  sprayed 
by  the  men  on  the  ground. 

Four  trees  in  one  side  of  this  orchard,  sanie  variety,  sarne  age  and 
size,  and  all  other  conditions  the  same,  were  left  unsprayed. 

Results. — ^^Tithout  a  single  exception  all  of  the  550  sprayed  trees 
came  uniformly  into  full  bloom,  while  the  trees  left  unsprayed  showed 
only  very  few  scattering  blossoms  and  these  badly  injured.     Figure  9 


Fig.  9.— Swell  iK-ar  orcliard  al  tiiiif  of  blooming.     Sprayed  trees.     ^AlLer  iwell.j 

shows  the  condition  of  a  sprayed  tree  at  blossoming  time.  The  550 
sprayed  trees  gave  a  yield  of  1,700  boxes  of  No.  1  pears  and  150 
boxes  of  No.  2  pears.  The  Xo.  1  pears,  at  an  average  net  price  of 
80  cents  per  box,  gives  $1,360,  and  the  150  boxes  of  Xo.  2  pears,  at 
50  cents  per  box,  gives  S75,  making  a  total  of  $1,435,  the  value  of  the 
crop  from  550  sprayed  trees,  or  practically  $2.60  per  tree. 


18 


HOW   TO    COXTROL   THE    PEAR    THRIPS. 


Figure  10  shows  an  unsp raved  tree  at  blossomin*!:  time.  The 
unsprayed  trees  gave  a  yiehl  of  less  than  one-foiirtii  box  per  tree,  all 
of  whicli  was  scarred,  misshapen,  and  unmerchantable;  but  counting 
them  as  Xo.  2  pears,  at  50  cents  per  box,  gives  a  return  of  about 
12^  cents  per  tree. 

According  to  Mr.  Swett,  the  spraying,  including  material,  labor, 
and  all  expenses  connected  with  the  operation,  cost  less  tlian  25- cents 


Fi<i 


10. -Swell  rK'ur  orchard  Jit  tiiiio  of  blooming.    Unsprayed  trees,  spravi-d  i)or(ion  of 
orehard  in  backKrtJinid.    (After  Swett.) 


per  tree  [or  the  550  trees.  TJiis,  plus  the  vahie  of  the  crop  (12.V  cents) 
from  the  check  trees, gives  37i  cents.  Subtracting  this  In-uu  the  S2.()(), 
value  of  the  crop  per  tree  in  the  sprayed  block,  leaves  a  net  gain  of 
$2,125  j)er  tree,  or  approximately  S225  i)er  acr(\  or  a  return  of  over 
1)00  per  cent  on  the  investment. 


HOW   TO   CONTROL   THE   PEAK   THRIPS.  19 

In  the  letter  giving  the  results  u])nn  which  these  itemized  figures 
are  based,  Mr.  Swett  continues: 

The  results  from  sprapng  on  prune  trees  wore  very  marked.  Owing  to  cross  limbs 
we  could  not  use  the  tower  in  sprajdng  the  prune  orchard.  The  crop  was  protected 
only  up  to  the  distance  from  the  ground  that  could  be  reached  by  the  spray  rods. 
We  wet  the  tops  of  the  trees  as  best  we  could,  but  could  not  drive  the  spray  into  the 
bud  and  flower  clusters  directly  from  the  nozzles.  Anyone  can  tell  where  the  rods 
reached,  for  above  the  line  there  is  no  crop,  and  below  that  line  the  limbs  mostly 
have  to  be  propped. 

CHERRIES,    SACRAMENTO    COUNTY. 

A  good  demonstration  showing  tlie  possibility  of  control  and  the 
commercial  advantage  by  spraying  cherries  was  given  by  ^Ir.  T.  W. 
Dean,  near  Courtland,  Cal.  Mr.  Dean  has  about  1 J  acres  or  180  trees 
in  bearing,  which  were  spra3^ed  upon  an  average  four  times  in  the 
spring  of  1910. (some  of  the  trees  sprayed  five  times  and  the  remainder 
only  three  times).  The  cost  of  the  spraying  was  approximately  $90, 
or  50  cents  per  tree.  Mr.  Dean  shii)ped  1,362  boxes  of  cherries  from 
the  180  trees,  or  7.56  boxes  per  tree,  which,  at  a  net  value  of  $1,196  per 
box,  gives  a  return  of  $1,619.95,  or  $8.99  per  tree. 

Sixty-five  trees  belonging  to  Mr.  I.  G.  Doty  and  immediately 
adjoining  the  above  orchard  were  not  sprayed.  The  65  trees  gave  a 
yield  of  43  boxes,  averaging  practically  two-thirds  of  a  box  per  tree, 
or  a  cash  vahie  of  $0,798  per  tree.  Adding  this  to  the  cost  of  spray- 
ing, 50  cents  per  tree,  gives  $1.30  as  the  amount  to  be  deducted 
from  the  value  of  the  crop  per  tree  in  the  sprayed  orchard.  The 
difference  is  $7.49  per  tree,  or  approximately  $898.80  per  acre, 
the  net  gain  due  to  spraying  paying  over  1,400  per  cent  on  the 
investment. 

RECOMMENDATIONS. 

Spraying  is  by  far  the  most  satisfactory  means  for  controlling  the 
pear  thrips-  on  all  classes  of  deciduous  fruit  trees  in  California. 
However,  to  spray  successfully  involves  an  entirely  different  concep- 
tion of  the  oi)eration  than  as  ordinaiily  practiced  against  other  orchard 
insects.  Only  the  most  ellicient  spray  materials  should  be  used, 
namely,  the  combination  of  distillate-oil  emulsion  and  tobacco  extract 
or  distillate-oil  emulsion  and  nicotine  solutions.  The  spraying  must 
be  thoroughly  done  and  put  on  the  trees  when  the  thrips  appear  in 
numbers,  not  w^aiting  till  many  buds  have  been  destroyed.  It  is 
strongly  advised  to  use  power  machines,  and  growers  are  urged  to 
use  them  for  all  the  spraying,  and  to  have  a  tower  platform  elevated 
over  the  tank  so  that  one  man  can  thoroughly  drench  the  tops  of  the 
trees.  Figures  6  and  1 1  show  two  good  types  of  powder  outfits  at 
work.  It  is  absolutely  necessary  to  use  high  pressure — from  150  to 
200  pounds — and  only  angle  nozzles  should  be  employed,  and  these 


20 


HOW   TO    CONTROL   THE   PEAR    THKIPS. 


must  be  held  close  to  the  biul  clusters  to  force  the  spray  directly  into 
the  ends  of  the  huds.  This  is  absolutely  necessary  to  secure  good 
penetration  and  get  satisfactory  results.  Plenty  of  material — 3  to  5 
gallons  per  tree  for  pears,  depending  on  the  size  of  the  tree — should  be 
used;  more  liquid  is  required  for  hirge  prune  trees;  large  cherry  trees 
may  require  7  to  8  gallons  per  tree  for  satisfactory  results.  Only  two 
rows  should  be  sprayed  at  a  time,  using  three  men,  one  on  the  tower 
to  spray  the  tops  of  the  trees,  thus  reaching  all  buds  pointing  u})ward, 
and  two  men  on  the  ground  (one  to  each  row)  to  spray  the  lower 
buds  and  those  pointing  downward  or  laterally. 


^--V 


^m^i,'^^Mi^ 


.■■.i:---' 


Fig.  n.— Power  outfil  ready  fjr  use  in  sprayiiii,' expt>riinenls  in  pear  orilmrds,  Contra  Costa  County, 

Cal.,  I'.iU).     (Original.) 


TIMING    THE    APPLK  ATIOXS. 

The  spraying  must  ])c  done  on  time,  and  for  best  resuUs  all  the  trees 
should  be  treated  within  a  few  days.  During  the  season  of  1910  more 
of  the  failure  to  get  satisfactory  results  was  due  to  lateness  of  ni)i)lica- 
tion  than  to  any  other  one  cause.  Thrips  were  in  the  trees  and  in 
great  numbers  before  many  of  {\w  growers  ])m-chase(l  tlu^ir  s))raying 
supplies,  and  in  many  cases  half  the  buds  weic  entii(dy  desti'oycd  and 
the  others  badly  injured  before  th(»  trees  had  Ixmmi  giv(Mi  even  the  lirst 
application.  The  growei'  should  have  (everything  in  I'cadiiuv^s,  all 
materials  on  hand,  concentrated  emulsion  mach'  u|),  and  spray  machin- 
ery in  j)erfect  working  or(h'r  by  the  lirst  of  March  and  have  all  other 
orchard  woik  in  such  sha|)e  that   when  the  thiips  appear  in  numl)ers 


HOW    TO   CONTROL   THE   PEAR   THRIPS.  ^1 

the  spraying  may  be  done  at  once  and  before  the  buds  have  been 
seriously  injured  by  the  feeding  of  the  adults.  The  grower  should 
have  enough  spray  machines  to  cover  the  orchard  quickly.  At  least 
one  good  power  outfit  is  necessary  for  every  30  acres  of  orchard. 

SCHEDULE    OF    APPLICATIONS. 

In  badly  infested  orchards  three  applications  are  necessary  the 
first  year  for  controlling  the  pear  thrips.  Two  of  these  sprayings 
should  be  directed  against  the  adults  and  one  against  the  larvse,  and 
to  obtain  satisfactory  results  must  be  timed  properly. 

First  application. — The  first  spraying  should  come  as  soon  as  the 
thrips  can  be  found  on  the  trees  in  numbers.  This  will  usually  be 
the  first  two  or  three  days  of  March,  just  as  the  earliest  buds  are 
separating  slightly  at  the  tips.  In  figures  12,  13,  and  14  are  shown 
photographs  of  the  more  advanced  buds  of  Bartlett  pear,  Imperial 
and  French  prunes, 
and  Black  Tartarian 
cherry,  which  were 
taken  at  time  of  first 
application. 

Second  applica- 
tion.— The  second 
spraying,  whichis  also 
for  adults,  should 
come  from  four  to 
ten  days  after  the 
first, depending  some- 
what on  VarietV  of  ^'"-  12.— Bartlctt  pear  cluster  buds  showing  stage  of  earliest  buds  at 
p       .,  ,  „  " ,        ,  lime  of  first  spraying  against  thrips.     (Original.) 

rruit,    stage    or   bud 

development,  and  rapidity  of  emergence  of  thrips  from  the  ground. 
On  pears  this  will  usually  be  just  as  the  earliest  cluster  buds  are 
spreading,  and  on  prunes  and  cherries  when  the  tips  of  the  petals  first 
begin  to  show. 

Both  of  these  applications  are  important  and  necessary  to  insure 
the  pnxkiction  of  a  good  croj)  of  uninjured  blossoms.  The  nozzles 
should  be  held  close  to  the  bud  clusters  and  the  spray  directed  into 
the  ends  of  tlie  buds.  This  makes  it  necessary  that  the  spraying  be 
done  mostly  from  above. 

Third  application. — The  third  s})raying  is  for  larvae  and  properly 
comes  just  as  most  of  the  petals  are  falhng  from  the  trees,  depending 
somewhat  upon  the  variety  of  fruit.  In  any  case  the  small,  w^hite, 
active  larvae  can  be  easily  seen,  and  when  they  first  become  abun- 
dant spraying  should  be  done.  In  this  larval  spraying  on  cherries 
and  ])runes  where  tlu^re  is  a  large  amount  of  leaf  surface  exposed,  the 


22 


HOW   TO   CONTROL  THE   PEAR   THRIPS. 


spray  should  be  directed  first  against  the  underside  of  the  leaves, 
beginning  with  the  lowest  branches  and  spraying  upward.  Most  of 
the  larvae  are  feeding  on  the  under  surface  of  the  leaves,  and  spraying 
the  upper  surface  first  would  serve  to  knock  the  larvae  from  the  trees 
without  their  coming  into  contact  with  the  spray.  Angle  nozzles  of 
the  iyY*e  shown  in  figure  15,  giving  coarse,  penetrating  spray,  should 
be  used  for  all  applications. 

MATERIALS    TO    USE. 

The  combination  of  3  per  cent  homemade  distillate-oil  emulsion, 
made  from  raw  distillate,  32°  to  34°  Baume,  and  the  nicotine  solutions. 


a  h 

Fig.  n.—a,  French  prune   buds;  b,   Inipt^rial  prune   buds;   stiowinR  stago  of  earliest 
buds  at  time  of  first  application  against  thrips.     (Original.) 

is  given  ])referenco  over  all  other  s])rays  used  so  far.  To  dilute, 
measure  out  5 J  gallons  of  the  stock  emulsion  for  each  100-gallon 
spray  tank,  or  1 1  gallons  for  a  2()()-gall()n  tank;  start  the  engine;  ])our 
the  stock  cinulsiou  into  the  s])ray' tank,  and  while  the  agitator  is 
nmning,  add  the  \vat(M-  to  fill  u])  the  tank,  ])iitting  in  the  strong 
nicotine  solution  last  and  after  the  stock  emulsion  has  been  diluted. 
Foi-  spraying  in  the    inlciior  counties  add   to  this  dilute  oil-emulsion 


HOW    TO    CONTROL   THE    PEAR    THRIPS. 


23 


commercial  tobacco  extract  No.  1,  which  is  a  dark,  ahiiost  viscous 
Hquid  containing  2.75  per  cent  nicotine,  at  the  rate  of  1  to  75;  or 
tobacco  extract  No.  2,  which  is  a  H^rht-colored  hquid  containing  40 
per  cent  of  almost  nonvolatile  nicotine  at  the  rate  of  1  to  1,500,  or  a 
fraction  more  than  a  pint  to  a  200- 
gallon  t  ank.  This  form  of  the  nicotine 
has  been  higldy  efficient  and  will  in 
all  probability  be  more  satisfactory 
than  the  former.  By  reason  of  its 
greater  concentration  the  handling 
and  transportation  charges  will  ])e 
much  less ;  also,  the  nicotine  contained 
in  this  preparation  is  much  less  vola- 
tile, thus  allowing  the  use  of  a  smaller 
amount  of  actual  nicotine  in  the  dilu- 
tion, as  it  remains  an  active  killing 
agent  for  a  longer  time  on  the  trees. 
In  Santa  Clara  County  greater 
dilutions  than  these  have  been  found 
to  be  satisfactory,  due  most  likely  to 
different  climatic  conditions,  evapo- 
ration there  being  much  less  at  this 
time  than  in  the  interior  counties 
where  the  atmosphere  is  drier.  Grow- 
ers in  the  Santa  Clara  Valley  are 
advised  to  use  the  3  ])er  cent  distillate-oil  emulsion,  with  tobacco 
extract  No.  1  added  at  the  rate  of  1  to  100  or  tobacco  extract  No. 
2  at  the   rat(»   of    1    to  2.000.     These  recommendations  hold  for  all 

thri])s  sprayings,  for  both  adults  and 
larva^  and  on  all  varieties  of  deciduous 
fniits  attacked  by  the  ])earthrips.  No  or- 
chards should  be  sprayed,  however,  when 
the  trees  are  in  full  bloom.  All  spraying 
for  adults  should  be  done  before  the  blos- 
soms appear  and  spraying  for  larvae  after 
a  large  proportion  of  the  petals  have 
fallen. 

In  the  prune  orchards  of  Santa  Clara 
Valley  deep  fall  plowing  and  cross-plow- 
ing has  proved  a  valuable  and  profita- 
ble aid  in  controlling  th{^  tlirips.  Those  who  can  do  so  are  strongly 
advised  to  irrigate  their  orchards  in  September  or  October,  and  when 
the  soil  is  in  ])roper  condition  ])low  with  disk  plows  to  a  depth  of  7  or 


Fig.  14. — Buds  of  Black  Tartarian  cherry  at 
time  of  first  application  against  thrips. 
About  one-half  natural  size.    (Original.) 


Fig.  15.— An^le  nozzle  of  the  large  cham- 
ber type  used  in  spra>ing  experiments. 
(Original.) 


24  HOW    TO    CONTROL   THE    PEAR   THRIPS. 

<S  inches  and  harrow,  then  cross  plow  8  to  9  inches  dee])  and  liarrow 
ao:ain.  All  })lowino:  should  be  done  during  the  months  of  October  and 
Xovember.  Durins:  this  season  the  thrips  are  passmg  through  tlie 
tender  ])U})al  stage  and  are  more  easily  kilLul  by  mechanical  means 
than  at  any  other  season  of  the  year. 

Plowing  has  not  proved  satisfactoiy  as  even  a  i)artial  means  of 
controlling  the  thrips  in  the  pear  orchards  of  the  interior  counties. 
This  is  due,  perhaps,  to  several  conditions,  one  of  which  is  the  differ- 
ent ty})e  of  soil,  and  another,  the  fnct  that  the  area  of  soil  infested 
with  thrips  around  })ear  trees  is  very  nuicli  less  than  around  j)rune 
trees,  the  branches  of  which  spread  farther,  covering  a  greater  surface 
of  ground.  The  larva^  in  leaving  the  trees  fall  to  the  ground  directly 
from  the  foliage  and  young  fruit,  rather  than  crawl  down  the  triudvs 
of  the  trees;  hence  in  a  prune  orchard  they  are  more  widely  distrib- 
uted throughout  the  soil  between  the  trees  and  can  be  reached  by  the 
plows,  while  in  a  pear  orchard  most  of  the  larvae  in  the  ground  are 
close  around  the  base  of  the  trees. 

SUMMARY. 

The  pear  thrips  can  be  controlled  by  thorough  spraying  on  any 
variety  of  the  deciduous  fruits  grown  in  the  infested  areas  of  Cali- 
fornia. 

The  sprayings  necessary  to  control  the  thrips  are  expensive,  but  the 
outlay  of  money  and  labor  gives  large  returns.  Many  experiments 
in  spraying  have  given  net  returns  of  from  SI 00  to  $600  j^er  acre  more 
than  was  secured  from  adjoining  untreated  areas. 

The  thrips  work  rajridly  and  may  destroy  all  ])ros])ects  of  a  crop 
in  less  than  a  week's  time.  Spraying,  to  be  successful,  must  be  done 
thoroughly  and  at  the  time  to  kill  the  thri])s  before  the  fruit  buds 
have  been  destroyed. 

Those  who  can  do  so  successfully  are  advised  to  irrigate  aiul  j)low 
in  the  fall.  This  is  to  be  followed  by  thorough  s])raying  the  follow- 
hig  spring. 

When  the  tlu'ips  begin  to  a])pear  on  the  trees  in  numbers,  spraying 
should  be  done  tliorougldy,  using  high  ])ressure,  holding  nozzles  ck)se 
to  buds,  and  directing  the  spnn/  dtrecth/  Into  the  ends  of  the  huds,  and 
not  against  the  sides. 

Orowers  should  not  attempt  to  s])ray  too  many  trees  with  one 
machine.  More  i)r()fitabh»  returns  will  be  gained  by  spraying  half  of 
the  orchard  thoroughly  and  at  ihv  proper  tiuics  than  l)ysj)raying  all  the 
orchard  ])()()rly  oue  time.  Ivesuhs  of  the  work  iii  1909  and  1910  show 
conclusively  that  one  application  is  not  suflicient  when  the  thrij)s  are 
ahunchml . 

o 


UNIVERSITY  OF  FLORIDA 


III 


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